As is well known, railroads are based on trains running on parallel metal rails. The rail road includes flat-bottom steel rails supported on timber crossties that are perpendicular to the rails. The ties are laid on crushed stone ballast. Each rail is placed on a tie plate disposed between the crosstie and the rail. The rail is held down to the crosstie with spikes that are driven through the tie plate to the crosstie. Additional tie anchors may be used to join the rail to the crosstie. The crosstie transfers the loads from the rails to the ballast and the ground underneath and holds the rails to the correct gauge. Typically, crossties are timber treated with creosote, copper-chrome-arsenic, or other wood preservative. The purpose of the ballast is to support the ties and allow some adjustment of their position, while allowing free drainage.
Railroads require periodic maintenance and replacement of worn out components such as crossties. For example, the crossties must be periodically inspected and replaced to maintain the rail gauge as well as insure the track transfers load. Replacement of crossties therefore must be performed quickly with a minimal amount of disturbance to the rails.
Currently, replacement of ties involves a tie gang that is a long series of machines that together march along the track, replacing bad crossties with new ones. From front to back, a tie gang includes machine operators to operate a sequence of machines such as spike pullers, spike reclaimers, tie cranes, tie extractor(s), anchor spreaders, tie cranes, tie inserters, tampers, plate placers, spike drivers, and surfacing machines to tamp the track and groom the ballast. There are also numerous workers on foot, handling tie plates and dealing with anomalies that come up where the machines have trouble. Old ties are marked with paint ahead of a tie gang, so the workers know which ties are to be replaced. New ties are typically distributed in bunches by another set of machines. Typically, this is done with a standard excavator running on top of a series of gondolas to bring the bunches of new ties near the rails. Near the front of the tie gang, a tie crane is used to distribute the bunches of ties so that a new tie is positioned next to each old tie that is to be replaced.
Currently, a “conventional” tie changing machine is used that operates by extracting ties with a mechanical arm while the rails are lifted above the tie to be pulled out. An example of a conventional tie changing machine is the TR-10 Tie Exchanger manufactured by Harsco Rail of Columbia, S.C. In order for the TR-10 to function, the spikes or clips must first be removed from the tie that is to be replaced. The conventional tie changing machine such as the TR-10 discards the tie plates and therefore requires a worker to manually pick up the tie plates and reposition them before the new ties may be inserted.
Following the tie removal, other, separate machines are used to spread the anchors and carefully position a new tie in line with the open crib. Additional conventional tie changing machines such as the TR-10 are used to insert the new ties. The inserters are followed by a tamping machine, additional laborers who reposition the tie plates on the new tie, and finally a plate inserter/rail lifter that slides the tie plates into their final position.
Thus, there is a need for a combined tie changing machine that can simultaneously hold the tie plates, spread the anchors, pull out the old tie, and insert a new tie, to save labor and machine costs. There is a further need for a tie changing machine having a similar construction as to existing excavators in order to facilitate the tie changing operation. There is a further need for a tie changing machine that is self-propelled and may remove ties from either side of a set of rails.